An Active Thermal Control Scheme of Three-level NPC Inverters

This paper focuses on reducing power loss and the unbalance issue of power loss distribution of power devices in three-phase three-level neutral-point-clamped (NPC) inverters. Firstly, the topology and commutation path of the NPC inverters are analyzed. Secondly, according to the characteristics of different loss distribution of the inverter at high and low switching frequencies, an efficient active thermal control scheme with hybrid switching frequency is proposed. The scheme can ensure the total harmonic distortion (THD) of the line current, but also reduces power loss of each power device in the NPC inverter. As a result, the loss unbalance problem of the inverter is effectively relieved, and the maximum temperature difference between the internal and external power devices is reduced as well. Finally, the proposed method is verified on a low-power experimental platform, and experimental results have verified the effectiveness of the proposed method.